As the title states, my current Thinkpad goes through the shutdown sequence too quickly to even start playing a shutdown sound. I was hoping to see if there's any way to force a delay that would allow the sound to play or a similar remedy.

You might be able to do something with the settings under the XShutdown tab in the Desktop properties (right click the desktop) or even add a small script to play the sound in the Xshutdown folder (create it in the above tab).

I'm not an ArcaOS user, nor are all OS changes publicly known: append a few seconds of silence to the sound file? Use one of the lesser shutdown utilities to play an own sound with e.g. Rexx (and MCPAPI.DLL), wait for it to finish and - if still needed - pause for a few milliseconds?

If the OS doesn't wait now, then appending silence may be useless. Instead of a test with a prefix or suffix of silence, you'd better try an existing file (e.g. a song) which lasts longer first.